Liquid crystal projectors have already been proposed in which liquid crystal panels are used (Unexamined Japanese Patent Publication SHO 61-150487.
The proposed projector is so adapted that three kinds of light signals R, B and G subjected to color separation are each passed through a liquid crystal panel for modulation with image data, then superposed and projected by a single projection lens on a screen in front of the lens.
Since the screen must be disposed in front of the projector, a sufficient space is required between the projection lens and the screen in front thereof. However, depending on the shape of the room wherein the projector is to be installed, such a sufficient space is not always available.
With reference to FIG. 8, the conventional liquid crystal projector has a light source 2 which comprises a metal halide lamp 25 and which is fixed in a central opening 11 of a parabolic reflector 1 with a ceramic adhesive 14.
Although having high luminance, the metal halide lamp has a shorter life than other lamps and needs to be replaced in about 2000 hours. The replacement of the metal halide lamp has the problem of an increased cost since the lamp is replaced along with the reflector fixedly carrying the lamp.
With respect to the liquid crystal panel which it is desired to operate at a temperature of up to 50.degree. C., polarizing plates, which are arranged in front and rear of the panel, become heated to a temperature 30.degree. C. higher than the atmospheric air, for example, at a polarization ratio of 40%. The heat is transferred to the liquid crystal panel, raising the temperature of the panel to above 50.degree. C. to possibly break the panel.
To obtain a high contrast ratio, the liquid crystal panel usually used is of the normally white type. Liquid crystal panels of this type have a sharp preference angle of field (about 6 degrees), such that the light deviating from this angle results in a markedly reduced contrast ratio.
As shown in FIG. 11, therefore a liquid crystal unit 5 in the form of an assembly of liquid crystal panel 50, polarizing plates 54, 55 on the incident and emanating sides, and condenser lens 56 is conventionally positioned as inclined at about 6 degrees with respect to a plane perpendicular to the optical axis (Unexamined Japanese Utility Model Publication SHO 64-30978). Nevertheless, the polarizing plates 54, 55 on the incident side and the emanating side satisfactorily serve as a polarizer and an analyzer only when light impinges thereon perpendicular thereto, whereas the polarizing plates in the conventional arrangement are inclined at about 6 degrees with respect to the plane perpendicular to the optical axis and therefore fail to operate propertly, consequently producing images of poor contrast.